A dose-volume histogram (“DVH”) is a graphical summary output from a radiation treatment planning that summarizes the distribution of the computed radiation doses delivered to a given structure. The most frequently used type of DVH is the cumulative DVH. Unless otherwise specified, a DVH without other mention refers to the cumulative DVH. Usually by convention the ordinate, y-axis, represents the structure's volume as a percentage or as a proportion (relative volume), and the abscissa, x-axis, represents the absolute dose. The DVH plots the volume receiving a dose greater than or equal to the corresponding dose represented on the x-axis. The DVH curve displays on the ordinate axis the percent or fraction volume of the structure irradiated in excess of the dose specified on the abscissa.
The major utility of the DVH is to evaluate whether a treatment plan would be associated with excess toxicity and/or with inadequate dose to control a tumor. Sets of DVH constraints and specifications of dose-volume requirements can be defined prior to conducting a radiation treatment plan. Comparison of the DVH between different treatment plan alternatives is a cornerstone in the radiation treatment planning process. International recommendations specify selected DVH points for reporting patients' treatment plans, such as the Dmean/Dmin/Dmax, i.e., the mean/minimum/maximum dose received by a structure, respectively. Or D2%, D50%, D95%, D98%, the dose received by 2%, 50%, 95%, 98% of the volume of the structure, respectively.
In the constructed example of FIG. 1A, the D95% would be found by drawing a horizontal line at the volume y=0.95, locating its intersection with the curve, and reading the vertical projection on the x-axis, which in this case is 32.8 Gy. Hence, the report would say D95%=32.8 Gy. Alternative ways of reporting can, equivalently, use volume-dose points such as V20 Gy or D95%, i.e., the volume of the structure receiving in excess of 20 Gy or in excess of 95% of the prescribed dose, respectively. Reading the Vxx mirrors reading the Dyy. In FIG. 1A, where the prescribed dose is 50 Gy, the V20 Gy equals 1 (100% of the volume), and the D95% corresponds to V47.5 Gy (47.5 Gy is 95% of 50 Gy), which from the curve equates 0.5, i.e., 50% of the volume.
Except for Dmean, the various doses Dyy or volumes Vxx presented above are selected points of the DVH curve for a structure. These points might or might not be representative of the DVH curve. Rather than focusing on selected dose-volume points, the present invention considers how the full DVH curve differs from a given dose A specified as reference. The difference is measured as the area between the actual DVH and the specified dose A. Herein, the specified dose A is a single dose value, for example a prescription of a uniform dose of 50 Gy to the structure. The does A may be any user-specified set of doses or dose-range, for example the prescription of a dose varying from 40 to 60 Gy to the structure. Since the difference can be in excess or in lack, which could generate negative area values, the absolute value of the deviation is used. This area is herein referred to as the mean absolute dose deviation (“MADD”) of the DVH from the dose A.
Any feature or combination of features described herein are included within the scope of the present invention provided that the features included in any such combination are not mutually inconsistent as will be apparent from the context, this specification, and the knowledge of one of ordinary skill in the art. Additional advantages and aspects of the present invention are apparent in the following detailed description and claims.